Portable computers such as tablet computers are thin and light to be carried by the users and have computing capability similar to the general personal computers. Consequently, portable computers are gradually loved by the user and widely found in the market. Generally, during operations, the tablet computer lies flat on the desk surface. For adjusting the tilt angle of the tablet computer, the tablet computer should be leant against other supporting article so as to be supported by the supporting article. The way of supporting the tablet computer is troublesome because it is time-consuming for the user to find out the proper supporting article. Since the tablet computer is not equipped with a physical keyboard, characters are inputted into the tablet computer by using the virtual keyboard shown on the touch screen, or in a handwriting means, or in a voice input means. Due to the size limitation of the tablet computer, the virtual keyboard is usually very small. In addition, since the arrangement of the virtual keyboard is different from the general keyboard, it is inconvenient to operate the virtual keyboard. Whereas, the character recognition rate of the tablet computer in the handwriting means or the voice input means is usually unsatisfied. In most circumstances, the user needs to correct the character shown on the virtual keyboard or even re-enter the character. For solving these drawbacks, many supporting devices and external keyboards for the tablet computers have been introduced into the market.
Please refer to FIGS. 1A, 1B and 1C. FIG. 1A is a schematic exploded view illustrating an electronic device supporting mechanism according to the prior art. FIG. 1B is a schematic perspective view illustrating the electronic device supporting mechanism of FIG. 1A and located at a supporting position. FIG. 1C is a schematic perspective view illustrating the electronic device supporting mechanism of FIG. 1A and located at a storing position. The supporting mechanism as shown in FIGS. 1A, 1B and 1C is disclosed in for example U.S. Pat. No. 7,059,576.
As shown in FIG. 1A, the electronic device supporting mechanism 1 comprises a base 11, a supporting arm 12, a stepless shaft 13, a supporting block 14, a supporting plate 15 and a keyboard 16. The base 11 comprises a first pivoting structure 11a, a second pivoting structure 11b and a receptacle 11c. The supporting arm 12 comprises a first pivotal end 12a, a fixing part 12b and two sliding grooves 12c. The supporting plate 15 comprises a first coupling part 15a and a second coupling part 15b. 
Please also refer to FIG. 1B. The supporting arm 12 is pivotally coupled to the first pivoting structure 11a of the base 11 through the first pivotal end 12a. The stepless shaft 13 is disposed on the fixing part 12b of the supporting arm 12. The supporting block 14 is disposed on the stepless shaft 13. The both ends of the first coupling part 15a at the upper edge of the supporting plate 15 are inserted into the sliding grooves 12c of the supporting arm 12. The second coupling part 15b at the lower edge of the supporting plate 15 is pivotally coupled to the second pivoting structure 11b of the base 11. The keyboard 16 is accommodated within the receptacle 11c of the base 11.
In a case that the electronic device supporting mechanism 1 is located at the supporting position (as shown in FIG. 1B), an electronic device may be placed on the supporting block 14. In addition, by adjusting the angle of the supporting block 14 through the stepless shaft 13, the viewing angle of the electronic device is changeable.
In a case that the electronic device supporting mechanism 1 is no longer used by the user, the both ends of the first coupling part 15a at the upper edge of the supporting plate 15 are moved downwardly along the sliding grooves 12c, and then the supporting arm 12 is pressed down until the supporting plate 15 and the supporting arm 12 are both in close contact with the base 11. Then, the supporting block 14 is rotated to lie flat on the supporting plate 15 (see FIG. 1C). Under this circumstance, the electronic device supporting mechanism 1 is located at the storing position.
From the above discussion, the electronic device supporting mechanism 1 is capable of supporting the external electronic device through the supporting arm 12, the supporting block 14 and the supporting plate 15 and capable of adjusting the viewing angle of the electronic device through the stepless shaft 13.
However, the conventional electronic device supporting mechanism still has some drawbacks. For example, the supporting arm, the stepless shaft, the supporting block, the supporting plate and the keyboard of the conventional electronic device supporting mechanism are all exposed outside. Consequently, during the process of carrying and moving the electronic device supporting mechanism, the supporting arm, the stepless shaft, the supporting block, the supporting plate or the keyboard is possibly entangled by other foreign articles and the problem is difficultly found by the user. When the electronic device supporting mechanism is removed by the user, the foreign article is readily hurt, or even the supporting arm, the stepless shaft, the supporting block or the supporting plate is suffered from deformation fracture, or the keys of the keyboard are detached. Moreover, the symbols marked on the keys of the keyboard are possibly worn away and difficult to be identified. Under this circumstance, the use life and the carrying convenience of the electronic device supporting mechanism will be impaired.
Therefore, there is a need of providing an improved electronic device supporting mechanism so as to obviate the drawbacks encountered from the prior art.